base/test/histogram_tester.h: Add a way to query a whole family of related

base/test/histogram_tester.h

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef BASE_TEST_HISTOGRAM_TESTER_H_
 #define BASE_TEST_HISTOGRAM_TESTER_H_
 
 #include <map>
 #include <string>
 
@@ skipping 29 matching lines @@
   void ExpectBucketCount(const std::string& name,
                          base::HistogramBase::Sample sample,
                          base::HistogramBase::Count expected_count) const;
 
   // We don't know the values of the samples, but we know how many there are.
   // This measures the diff from the snapshot taken when this object was
   // constructed.
   void ExpectTotalCount(const std::string& name,
                         base::HistogramBase::Count count) const;
 
+  // Finds histograms whose names start with |query|, and return a text

[Ilya Sherman, 2015/06/23 00:57:40]

nit: "return" -> "returns"

+  // representation of any new samples added since the creation of this object.
+  // Histograms that are unchanged are omitted from the result. The return value
+  // consists of lines of the form:
+  //
+  //   - "My.Statistic.Name[2]=5" (for linear, boolean, and enum histograms)
+  //   - "My.Statistic.Name=5"    (for other kinds of histograms)
+  //
+  // In the above example, 2 is the bucket min and 5 is the count. For nonlinear
+  // histograms, only the total across all buckets is shown, under the
+  // assumption that the inputs to nonlinear histograms -- sizes and times,
+  // commonly -- may be hard for a test to predict.
+  //
+  // This is useful for cases where the code under test is choosing among a
+  // family of related histograms and incrementing one of them. Typically you
+  // should pass the result of this function directly to EXPECT_EQ, which does a
+  // good job of formatting human-readable diffs of multi-line strings.

[Ilya Sherman, 2015/06/23 00:57:40]

nit: You should probably mention somewhere that the returned list is sorted
alphabetically.

+  std::string GetTotalCountsForQuery(const std::string& query) const;
+
   // Access a modified HistogramSamples containing only what has been logged
   // to the histogram since the creation of this object.
   scoped_ptr<HistogramSamples> GetHistogramSamplesSinceCreation(
       const std::string& histogram_name);
 
  private:
   // Verifies and asserts that value in the |sample| bucket matches the
   // |expected_count|. The bucket's current value is determined from |samples|
   // and is modified based on the snapshot stored for histogram |name|.
   void CheckBucketCount(const std::string& name,
@@ skipping 12 matching lines @@
   // lifecycle. This instance takes ownership of the samples, which are deleted
   // when the instance is destroyed.
   std::map<std::string, HistogramSamples*> histograms_snapshot_;
 
   DISALLOW_COPY_AND_ASSIGN(HistogramTester);
 };
 
 }  // namespace base
 
 #endif  // BASE_TEST_HISTOGRAM_TESTER_H_